This is the dipping schedule for ceramic shell investment casting that we use at Cal State University Long Beach. This is just one example of a dipping schedule, I've talked to a number of casters and they all seem to have their own. In my home studio I modify the dipping a bit based on the piece, but the one below is pretty student proof (if they follow it). Assuming the schedule is followed, the two main factors to a solid crack-free shell is allowing the shell to fully dry between dips and a quick burn-out. We preheat the burnout kiln to over 500°F before putting in the shells. Since we started doing this, cracks have almost completely disappeared. For pieces larger then 25 lb. or so, add an extra layer of number 3 stucco for every 7-10 lb or so. This also applies to large flat areas.

Investment Dipping Procedures

Before you start investing

1. Weigh the wax piece (including sprues and cup) and record the weight on the sculpture data sheet.

2. Check that all sprue, vent, and runner joints are properly welded

3. Show the instructor your piece and make sure he OK’s your sprueing and venting.

4. Draw a picture of your piece so that you and others will be able to recognize it once it is invested.

5. Shellac the piece with one medium coat. Use shellac only (not lacquer or acrylic).

6. You are now ready to start dipping.

Investing

Dipping for smaller pieces

1. Hold the piece parallel to the floor and cradle in both hands.

2. Gently dip the piece into the slurry and rotate for about 30 seconds.

3. Lift up the piece and allow it to drain completely until it stops dripping. Rotate occasionally to assure an even coat and that there are no puddles in crevasses.

Dipping for larger pieces

1. Put the metal grate on the slurry tank.

2. Rest the piece on the grate and use one or more of the following methods:

a. Using a cup pour slurry over the piece

b. Use a brush to paint slurry onto all surfaces.

c. Dip part of the piece and use methods a or b to coat the rest of the piece with slurry.

3. Allow the piece to drain completely until it stops dripping. Rotate occasionally to assure an even coat and that there are no puddles in crevasses.

Dip #1 & 2

1. Check the piece to be sure there are no loose pieces of wax.

2. Dip and drain the piece then put it on the shelf.

3. Check the slurry tank to make sure there are no pieces of wax that fell off your piece. Remove any pieces of wax with the strainer.

Dip #3 - #12

1. Follow the investment chart on the wall in the slurry room for the schedule of dips.

2. Sift the stucco in the appropriate stucco bin so it is clean. Create a flat bed to place your piece on.

3. Use the compressed air line (20 psi max pressure) to blow off any loose stucco from your piece.

4. Coat the piece with slurry and let it drain into the slurry tank until it no longer drips excessively. There should be an even coating of slurry on the whole piece, no puddles or dry spots.

5. Put the piece on the bed of stucco and sift more stucco onto it. Rotate the piece or throw stucco into it so that it is covered on all sides.

6. Wipe the stucco off from the top of the cup.

7. Place the piece cup down onto the shelves to dry.

8. Clean the stucco bin with the strainer and throw away any small globs or chunks.

9. Mark the time of the dip on your sculpture data sheet. If there were any unusual problems, mark them on your sculpture data sheet.

The Final Dip

1. Use slurry only, no stucco.

2. Allow the piece to dry for at least 12 hours before burnout.

Important Points to Note

Safety

• Use gloves to protect your hands. Slurry is composed of microscopic particles of silica that can seep into the skin and cause skin problems.

• Wear a dust mask.

Care of the Slurry Tank – If you don’t take care of it, it is your sculptures that may not cast properly.

• It is important to keep as much stucco as possible out of the slurry tank. Be sure to gently blow off any loose stucco with the air hose before you dip it.∑ On the front bottom of the slurry tank, there is a red line. It marks where the propeller is; do not put your piece into the propeller – especially if the motor is running!

• If possible, wait until the motor in the slurry tank turns off before you dip so the propeller will not hit your piece.

• You are responsible to keep the slurry tank clean of any wax particles. Check it after your first dip!

• Allow the slurry to drip off your piece while turning the mold. Do not let it get too dry or the stucco will not stick to parts of your sculpture causing thing areas in the mold.